1. Technical Field
The present invention relates to a printing apparatus such as an ink jet printer and a printing method.
2. Related Art
In the past, as a printing apparatus having a plurality of heads to perform printing, there were known printing apparatuses disclosed in JP-A-2007-320110, JP-A-2002-103598, and JP-A-2006-326856.
The printing apparatus disclosed in JP-A-2007-320110 includes two heads 8 and 9 for ejecting ink, as shown in FIG. 10. The heads 8 and 9 have nozzles 81 and 91, respectively. The nozzles 81 and 91 are each arranged at a predetermined pitch. The two heads 8 and 9 are disposed in two rows in a direction intersecting a transport direction of a sheet. Moreover, the pitch of the nozzles of the first row head is deviated by ½ of a predetermined pitch from the pitch of the nozzles of the second row head.
The printing apparatus disclosed in JP-A-2002-103598 includes heads for ejecting black ink, yellow ink, magenta ink, and cyan ink, respectively, and performs printing by ejecting the ink onto a print medium sequentially from the plurality of heads.
The printing apparatus disclosed in JP-A-2006-326856 includes a first row print head and a second row print head ejecting ink onto a print medium. The first row print head and the second row print head are disposed in zigzags.
In the printing apparatus disclosed in JP-A-2007-320110, however, the first row head 8 and the second row head 9 are disposed at a predetermined interval in a transport direction of a sheet. Therefore, it takes a certain time to eject ink from the nozzles 91 of the second row head 9 after the ink is ejected from the nozzles 81 of the first row head 8. For this reason, since the ink permeates into the sheet (print medium) and is dried during the certain time, it is considered that the ink is prevented from spreading. A method of disposing heater for making ink dry more rapidly between the first and second row heads may be taken into consideration.
Taking this configuration into consideration, the printing apparatus disclosed in JP-A-2007-320110 can ensure the maximum amount of ink to be ejected from the nozzles even upon performing high speed printing. Accordingly, it is possible to realize the high speed printing without deteriorating print density.
In the printing apparatus disclosed in JP-A-2007-320110, however, disposition precision of the heads 8 and 9 becomes worse as the disposition distance between the first row head 8 and the second row head 9 is larger. This is because the first row head 8 and the second row head 9 are disposed at the predetermined interval in the transport direction of the sheet. For this reason, it is necessary to make an improvement in position precision between dots of the ink ejected from the nozzles 81 of the first row head 8 and the dots of the ink ejected from the nozzles 91 of the second row head 9.
FIGS. 11A and 11B show print examples of a character printed by the printing apparatus disclosed in JP-A-2007-320110.
In FIGS. 11A and 11B, circles indicate dots formed by ejecting ink from the nozzles 81 of the head 8 and the nozzles 91 of the head 9. Numeral “1” in the circles represents the dots formed by the nozzles 81 and Numeral “3” in the circles presents the dots formed by the nozzles 91.
FIG. 11A shows a good example of the position precision of the dots fowled by ejecting the ink by the heads 8 and 9. In contrast, FIG. 11B shows a poor example of the position precision of the dots and shows that the precision of the dots of the ink cannot be ensured.
In such a circumstance, it is necessary to devise a printing apparatus capable of ensuring the position precision of the dots of ink upon printing a character or the like by a plurality of heads, while performing high speed printing.